10:1, you should use a 92 octane minimum, you could get away with it maby if you had aluminum heads. with 9.5:1 you could get away with 89. why get a lower compression and higher octane, you use higher octane for a higher compression. higher octanes are less prone to pre ignition than with the lower octane fuels that's why there used. when you build an engine/ car, always figure that speed costs money, how fast do you want to go?